Method and apparatus for producing filaments from vitreous material

ABSTRACT

A DROP OF VISCOUS MOLTEN VITREOUS MATERIAL IS EXUDED FROM AN ORIFICE COMMUNICATING WITH A SUPPLY OF SUCH MATERIAL. SO EXUDED, THE DROP WILL DESCEND UNDER THE INFLUENCE OF GRAVITY WHILE DRAWING BEHIND IT A LENGTH OF FILAMENT OF THE VITREOUS MATERIAL. THE DESCENDING DROP IS CONTACTED WITH A CURTAIN OF LIQUID WHICH IS BEING PROPELLED TRANSVERSELY TO THE DIRECTION OF DESCENT AT SUCH VELOCITY AS TO DEFLECT, ACCELERATE AND SEVER THE DROP AND PROXIMAL PORTIONS OF THE FILAMENT FROM THE REMAINDER OF THE LENGTH OF FILAMENT. THIS IS ACCOMPLISHED BY A LIQUID SUPPLY CONDUIT HAVING A PLURALITY OF LIQUID EJECTING NOZZLES WHICH FORCE THE FILAMENTS INTO A ROTARY FILAMENT DRAWING SURFACE.

Nov. 30, 1971 KElB 3,623,853

METHOD AND APPARATUS FOR PRODUCING FILAMENTS FROM VITREOUS MATERIAL FilOd. Aug. 29, 1969 SUPPLY MEANS S N A E M U P P U S INVENTjOR. HEINZ kEl 5 United States Patent O 3,623,853 METHOD AND APPARATUS FOR PRODUCING FILAMENTS FROM VITREOUS MATERIAL Heinz Keib, Wertheim am Main, Germany, assignor to Schuller, Werner Hugo Wilhelm, Munich-Grunwald,

Germany Filed Aug. 29, 1969, Ser. No. 854,134 Claims priority, application Germany, Sept. 7, 1968, P 17 96 143.2 Int. Cl. C03b 37/02 US. Cl. 65-2 15 Claims ABSTRACT OF THE DISCLOSURE A drop of viscous molten vitreous material is exuded from an orifice communicating with a supply of such material. So exuded, the drop will descend under the influence of gravity while drawing behind it a length of filament of the vitreous material. The descending drop is contacted with a curtain of liquid which is being propelled transversely to the direction of descent at such velocity as to deflect, accelerate and sever the drop and proximal portions of the filament from the remainder of the length of filament. This is accomplished by a liquid supply conduit having a plurality of liquid ejecting nozzles which force the filaments into a rotary filament drawing surface.

BACKGROUND OF THE INVENTION The present invention relates generally to the production of filaments from molten vitreous material, and more particularly to the production of filaments from molten glass.

It is already known to produce glass filaments by heating a glass to melting temperature, and dividing the resulting body of molten glass into a plurality of closely adjacent small streams each of which is drawn into the shape of a filament. For economic reasons, a great number of such filaments are drawn simultaneously and are located very closely adjacent one another in substantial parallelism. The production of the individual filaments is initiated when-either upon starting-up of the operations or subsequent to breakage of one of the filaments during operation-a drop of the molten vitreous material exudes from the point of origin of the filaments, for instance from a nozzle orifice communicating with the interior of a crucible which contains the mass of molten vitreous material. This drop descends under the influence of gravity in downward direction and draws after it a length of filament. Immediately upstream of the descending drop, the filament does not have its final cross-sectional area. Instead, a portion of the filament immediately upstream of the descending drop tapers in cross-sectional area in the upstream direction. The drop and this tapering portion may not be incorporated with the filaments being produced for various reasons which will be discussed in more detail subsequently. They must therefore be removed from the filament, and the latter must be drawn to its desired thickness, before it can be incorporated into the filament producing process, that is before it can be allowed to admix with other filaments produced by the same apparatus. The tapering portion is also often called spear.

For this purpose there is provided a so-called dofling apparatus. The known prior-art constructions of such apparatus are based on the principle of advancing the descending dro and upstream tapering portion to the circumference of a rotating dofling roller which, rotating at requisite speed, severs the drop and the tapering portion from the remainder of the filament, and draws the remainder of the filament down to the desired thickness. Once this thickness has been reached, the new filamentice which is now called a production filamentis severed from the filament portion which has been wound onto the dofler roller or a winding roller which cooperates with the doffer roller, and is automatically supplied to its proper position among the multitude of filaments which are being simultaneously produced by withdrawing molten vitreous material from the crucible or other supply of such material.

It was mentioned before that the drops and the tapering portions upstream thereof may not be allowed to admix with the production filaments. The reason for this is that the tapering portion has at various different longitudinal locations a plurality of different diameters which may be as high as or higher than ten or twenty times the diameter of the production filament. Evidently, under these circumstances, the tapering portion is both stiff and voluminous with reference to the production filament and will therefore adversely influence the softness and pliabllity of the intermediate product which may for instance have the form of a strand, :1 sliver, a glass fiber ribbon, a woven or non-woven web, or the like, or of the final product produced therefrom, such as glass fiber roofing, corrosion protection bandages, or the like. It is also possible, particularly when the products are subjected to pressure or bending, that these much stiffer tapering portions would cut the final product. Aside from this there is the fact that the apparatus which converts the intermediate product, for instance by coating it with a liquid medium or embedding it with corrosion protection or synthetic plastic materials, uses rotary elements such as rollers, drums, spools or the like. These elements can be damaged by the drops and the tapering portions which during operation of the apparatus and processing by the same would break. Finally, there is the additional consideration that drops and the tapering portions would tear adjacent production filaments if they were to be allowed to remain, rather than being separated.

The difficulty with prior-art approaches to the problem of separating the drops and tapering portions is in the fact that they are rather inflexible and do not therefore readily accommodate themselves to the configuration of the circumference of the doffing roller. This is particularly true in view of the fact that the doffing roller rotates at high speed and may even lead to the drops and tapering portions being bounced or deflected away from the roller periphery on contact therewith. To some extent this has been overcome in the prior art by providing guide skirts and protective skirts in the vicinity of the dofiing roller, but the provision of these elements in turn has created its own problems because their presence makes it diflicult to transfer the filament-once it has been separated from the drop and the tapering portionto its assigned place among the production filaments. On the other hand, if a drawing drum is used which rotates at high speed. for instance of the type disclosed in the Austrian Pat. No. 266,367, there is the additional disadvantage that any drops or tapering filament portions which may accidentally become mixed in which the production filaments, will shatter and be flung off in all directions upon contacting the circumference of the rotating drawing drum, thereby tearing large numbers of production filaments. This is difficult to overcome because in all known prior-art constructions utilizing dofiing rollers or doffing drums, the transfer of the filaments from the doffing roller or dofiing drum subsequent to separation of the drop and ta ering filament portionto the drawing drum necessitates that the latter and the dofiing drum be rather closely adjacent each other unless one is willing to resort to complicated, mechanically difficult and hard-to-service devices for transferring the filaments from the doffing roller to the drawing roller. Experience has shown, for instance, that when operating the devices disclosed in German Pat. No. 822,-

004 and Belgium Patent No. 639,800, drops and tapering filament portions which are separated from the filaments by the doffing drum, are not always flung off the periphery of the doffing drum, but instead at times are carried around by the dofiing drum and are then introduced into the gap between the doffing drum and drawing drum which exists because of the close proximity of the two drums; if this occurs, they can tear at least some of the production filaments which are being drawn by the drawing drum and can also damage the surface of the drawing drum which latter is a rather expensive item to manufacture.

Evidently, these problems are the greaterparticular ly when a drawing drum is used for drawing the production filamentsthe larger the output requirements for the apparatus are set. This, of course, is a continuing tendency because it would potentially serve to reduce the expenses involved and to provide for more economic manufacture of the vitreous filament. This is usually done by increasing the number of filaments which can be produced in an apparatus by arranging the production filaments not in a single row of adjacent filaments, but by arranging two or several such rows, and it is evident that the greater the number of production filaments involved, the greater are the dangers that larger numbers of production filaments will be damaged under the circumstances outlined above. Evidently, with each filament which is torn the problems are further increased, because when the filament is restarted a new drop and a new tapering filament portion form which must be removed and which potentially may cause further trouble. The problem is further aggravated if two or several filaments tear or are torn simultaneously so that, on re-starting, two or several drops and tapering filament portions are being produced simultaneously or non-simultaneously.

Experience has shown that it is usually advantageous to rotate the doffing roller with as high a speed of rotation as possible. The reason for this is to draw the newly-produced filament to the desired thickness as quickly as possible and to separate and fling off the drop and tapering filament portion as reliably as possible. However, it is necessary to maintain a certain speed differential between the rotation of the doffing roller and that of the drawing roller so that the new filament is drawn to substantially the desired thickness but thereupon engaged and drawn towards the circumference of the faster-rotating drawing drum by the rotating boundary layer which sweeps about the circumference of the drawing drum. 1

A further consideration is that the dofiing roller and associated rotary components must be precisely manufactured and balanced. To assure that they will properly operate, they must further be precisely journalled and lubricated, and they must be constantly supervised and maintained to keep them clean and to assure that they rotate at proper speed. Evidently, this constant supervision requires the constant attention of personnel, which is expensive at best.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to provide a method of producing a filament from molten vitreous material which is not subject to the aforementioned disadvantages.

An additional object of the invention is to provide an apparatus for carrying out the method.

A concomitant object of the invention is to assure the reliable separation and removal of drops and tapering filament portions.

A further object of the invention is to provide an apparatus capable of affording such operation which is simple in its construction and which requires at most very little maintenance.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of the invention resides in a method of producing filaments from vitreous material. This method, briefly stated, comprises the steps of exuding a drop of viscous molten vitreous material from an orifice communicating with a supply of such material, so that the drop will descend under the influence of gravity while drawing behind it a length of filament of said material. Thereupon, the descending drop and proximal filament portions of the length of filament are contacted with a curtain of liquid which is being propelled transversely to the direction of descent at such velocity as to deflect, accelerate and sever the drop and proximal filament portions from the remainder of the length of filament.

It will be seen, therefore, that the present invention avoids the use of any rotary components in connection with the removal of the drop and tapering filament portion from the remainder of the newly-started filament length.

Not only is this a very simple and very reliable manner of obtaining the desired results, it also requires little energy for operation of an apparatus based upon the concept of the present invention. In addition, the drops and tapering filament portions which heretofore have been a constant source of danger to the health of operating personnel, no longer pose this problem because they are shattered into readily removable granular state.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic partly sectioned side view of an apparatus according to the present invention;

FIG. 2 is a detail view, on an enlarged scale, showing the configuration of the exuded drop and the tapering filament portion upstream thereof;

FIG. 3 is a front view on an embodiment according to FIG. 1 and FIG. 4 is a partial View similar to FIG. 1, but on an enlarged scale and illustrating yet an additional embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing in detail, and firstly FIGS. 1 and 2 thereof, it will be seen that reference numeral 1 identifies a drawing drum which may be of entirely conventional cosntruction and which is well known to those skilled in the art. The drum 1 is elongated axially in direction normal to the plane of FIG. 1 and rotates in the direction of the arrow A. Supply means is diagrammatically illustrated and may be in the form of a crucible having in its bottom wall a plurality of outlet orifices (compare FIG. 2 where one such outlet is shown); the supply means may extend longitudinally of the drum 1 as illustrated and may have one or several rows of orifices from which filaments can be withdrawn. In known manner the supply means will contain a body of molten vitreous material. Production filaments, that is filaments which have already been freed of the drop and tapering filament portion, are constantly being withdrawn from each orifice associated with the supply means, by the drawing drum 1 onto which they may be wound to be removed from its circumference in form of threads. They can also be stripped off the circumference of the drum after less than a single convolution thereabout by means of a doctor blade 3 and a reversing arrangement 4 which is diagrammatically illustrated. In the latter case, the filaments are severed into the form of glass or vitreous fibers. If so, the boundary layer of air which is carried along by rotation of the drum 1 in the direction of the arrow A,

produces a stream of fibers identified by the arrow B and which can be recovered and further processed in any known manner to form a fiber mat, fiber ribbon, sliver or the like. This, however, does not form a part of the present invention.

Assuming, now, that the apparatus has been temporarily stopped and is now started again, or that one or more of the production filaments break for any reason whatever, new filaments must be started. This occurs when the respective orifice or orifices of the supply means exudes a drop of molten vitreous material which descends under the influence of gravity in downward direction. The configuration of the drop and of the tapering filament portion adjacent the drop 5 and identified with reference numeral 6, is shown more clearly in FIG. 2 where it Will also be evident that the drop 5 and the tapering filament portion 6 draw behind them a newly-started filament 7. The descending drop, which is maintained in suitable manner at a requisite distance from the drawing drum 1 so as not to be drawn against the same by the aforementioned rotating boundary layer, and which is also maintained at a similar distance from the production filaments 2 to avoid damaging the same, contacts in the region C a liquid curtain 8 which is projected under pressure transversely of the direction of descent. The width of the curtain 8 corresponds to the axial length of the drum 1, or may be selected differently in accordance with the prevailing requirements. In any case, contact of the drop 5 and the tapering filament portion 6 with this curtain 8 results in almost instantaneous acceleration which in turn causes the newly-started filament 7 to be drawn forwardly while at the same time it is being displaced in the direction of movement of the curtain 8 or of the inclination of the guide surface 9 which guides the curtain 8, in the direction of the arrow D.

When the newly-started filament 7 has reached approximately the dotted-line position 10, that portion of the filament 7 which has now come close enough to the circumference of the drawing drum 1, is drawn towards the circumference by the rotating boundary layer which sweeps about the circumference of the drum 1. Because the speed of the drum 1 and of the boundary layer 1s greater than the advancement of the filament 7, the latter is carried along the drum 1 and severed from the drop 5 and the tapering filament portion 6 which are carried away by the liquid of the liquid curtain 8.

It may happen occasionally that the drop 5 and the tapering filament portion 6 will not immediately become severed from the remainder of the filament 7 upon engagement of the same by the drawing drum. Should this occur, the filament will assume the position shown in chain lines and identified with reference numeral 11. To avoid difficulties under these circumstances the guide member 12 of the illustrated configuration is provided, and at the edge of this guide member the filament will immediately develop a loop and a sharp bend E whose development will result in immediate severing on the drop 5 and the tapering filament portion 6 of the remainder of the filament 7.

It will be appreciated that at the time the drop 5 and the tapering filament portion 6 contact the liquid curtain 8, they will not yet have solidified and will still be very hot because of the relatively short distance which they have traversed from the supply means to the liquid curtain 8. Accordingly, the sudden cooling which occurs on contact with the liquid curtain 8 results in shattering of the drop 5 and the filament portion 6 so that they fall apart in form of granules. These are then carried along by the liquid curtain 8. If desired, a screen 13 or analogous means may be provided for screening out the shattered particles from the liquid which may then be re-circulated in non-illustrated but conventional manner, whereas the screened-out particles may be removed and discarded, or be themselves re-circulated to the supply means for melting down. Removal of the screened-out particles may be 6 via a channel, a conduit or, as illustrated, a conveyor belt 14.

It will be appreciated that different liquids may be used for producing the liquid curtain, but water is most advantageous because it is least expensive. The liquid curtain 8 can be produced in various different ways, and these will suggest themselves to those skilled in the art. Reference numeral 15 diagrammatically suggests how the curtain 8 may be produced, in that it shows that a pipe or conduit can be provided which may be turnable about its longitudinal axis, the latter of course extending normal to the plane of FIG. 1. The pipe 15 will be provided with a single slot-shaped outlet nozzle extending over the entire width for which the liquid curtain 8 is to be produced, or it may be provided with a plurality of individual nozzles arrayed longitudinally of the pipe 15. The construction of such nozzles is not new and does not form part of the invention. However, it is emphasized that it may be advantageous to make at least some of the individual nozzles turnable so that the streams of liquid issuing from them may be directed towards the upper surface of the guide member 9 which is located below the water curtain 8 and inclined in the illustrated manner. The reason for this will be discussed below, but it is pointed out that instead of making certain of the individual nozzles turnable in this manner, they may also be fixedly oriented in this way.

As shown in FIG. 1, it is particularly advantageous to so direct the liquid curtain 8 that it will be propelled out of contact with the surface of the member 9 for as large a distance as possible, because its speed of propulsion is obviously the greater the less it is retarded as a result of frictional contact with the member 9. Advantageously, at least for the first third of its length-as seen with respect to the direction of movement upon issuing from the nozzles of the pipe 15-the liquid curtain should be propelled in parallelism or in substantial parallelism with the surface of the element 9 without contacting the same.

It is also shown that a cover member 16 is provided at the upper end of the element 9 which prevents decending drops which may for some reason have started a pendulum motion, from descending behin dthe pipe 15 and therefore behind the liquid curtain 8 where they would not be subjected to the intended treatment.

To protect the pipe 15, the same may be located in the space between the member 9 and the element 16 as shown in FIG. 1.

It will be appreciated that if individual nozzles are used on the pipe 15, which term here is intended to include the provision of simple bores or other apertures in the pipe 15 rather than separate nozzles, the streams of liquid issuing from the respective nozzles must so overlap that in the region C, as shown in FIG. 3, the water curtain is continuous and without interruption. The purpose of having some of the nozzles discharge their streams of liquid against the surface of the member 9, as shown in FIG. 4, is to have these streams sweep debris off this surface and constantly clean it.

It is well known that in prior-art constructions utilizing doffing rollers, descending drops frequently contact the guide elements which are intended to guide them to the doffing roller, and to adhere to these guide elements. The result of this is that they will of course no longer draw after them a new filament. Evidently, the filament portion which had already been drawn by the drop before the latter adhered to the guide element, will tear off at the outlet orifice of the supply means, and a new drop will exude and draw a new filament after it. However, the torn-off filament portion may frequently enter among the production filaments and either tear some of these or at least become admixed with them without any control being exerted. Furthermore, a residue adhering to the guide elements of course prevents subsequently descending drops from probably moving into contact with the doffing roller. This at times leads to significant disturbances in the proper operation of the apparatus. This prob lem is entirely-overcome with the present invention because the drops and the tapering filament portions are reliably severed and carried away in each and every case without having the possibility of adhering or accumulating anywhere. Even if such a drop or filament portion 6 should manage to pass through the water curtain and contract the surface of the member 9, the sudden cooling to which it has been subjected during passage through the water curtain 8 would prevent it from adhering to the element 9.

A further problem in prior-art constructions was the fact that at times the newly-started filament was able to pass into engagement with the drawing drum before its leading end, that is the drop and the tapering filament portion, had already been reliably engaged by the dofling drum. The result was that the drop and the tapering filament portion was ripped back to the drawing drum and became admixed with the production filaments with the disadvantages which had been mentioned earlier. This, also, is impossible when resort is had to the present invention because contact and sudden cooling of the drop and the tapering filament portion with the Water or liquid curtain 8 results in immediate breaking-up and severing of the drop and tapering filament portion from the remainder of the newly-started filament, while at the same time, a proper forward drawing of the new filament is guaranteed as a result of the acceleration imparted to it by the velocity of the liquid curtain 8.

It is advantageous to arrange the elements 9, and, if present, 16, in a pit provided in the floor on which the remainder of the apparatus is set up, in order to increase the distance by which the drops 5 must descend, and to increase the space between the axis of rotation of the drum 1 and the area C in which the drops 5 contact the liquid curtain 8. By resort to this, these features can be obtained without increasing the overall height of. the apparatus. It has been found that a relationship of approximately 1:221, measured from the orifice of the supply means to the axis of the drum 1, from there to the area C, and from there to the lowermost end of the element 9, provides reliable drawing forward and separation in accordance with the invention. In addition, when the arrangement is as just described, the debris resulting from shattering of the drops 5 and the filament portions 6 can be most readily separated from the flowing liquid and the latter be returned to the pipe 15. Of course, it will be appreciated without specific emphasis that suitable pumps are provided for circulating purposes and for imparting to the water the necessary velocity.

It is a highly desirable fringe benefit of the present invention that it solves or at least advantageously influences the air conditioning problem involved in the operation of equipment of the type under discussion. In the region of the drum 1 and above the same, there is enough moisture introduced into the air as a result of the production of the liquid curtain, that the conditioning of the air that was heretofore necessary may be eliminated or at least significantly reduced. Such conditioning heretofore was necessary because fibers of vitreous material, particularly glass, have a tendency to electrostatic charging with concomitant difficulties in the production as a result of conglomerations, erection of individual fibers and the like. The moisture content resulting from operation of an apparatus according to the present invention avoids this problem, or at least reduces it significantly.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in the production of filaments from vitreous material, it is not intended to be limited to the details shown, since various modifications and structural changes 8 may be made without departing in any way from the spirit of the present invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A method of producing filaments from vitreous material, comprising the steps of exuding a drop of molten vitreous material from an orifice communicating with a supply of such material, so that the drop will descend under the influence of gravity in a plane which is laterally spaced from a rotary filament drawing surface, while drawing behind it a length of filament of said material; and propelling a curtain of liquid transversely of said plane against the descending drop and proximal filament portions at a velocity requisite for severing said drop and proximal filament portions from the remainder of said length of filament, while deflecting said remainder out of said plane and into contact with said rotary filament drawing surface.

2. A method as defined in claim 1; and further comprising the step of drawing said remainder of said length of filament so as to withdraw additional molten vitreous material in filamentary form from said orifice.

3. A method as defined in claim 1, wherein said curtain of liquid is inclined in the direction of descent of said drop.

4. A method as defined in claim 1, said curtain of liquid having a predetermined length in direction transversely of said plane, and wherein said curtain of liquid is propelled freely through space over substantially one third of said predetermined length.

5. A method as defined in claim 1, wherein said curtain of liquid is composed of a plurality of discrete jets of liquid.

6. A method as defined in claim 5, a guide surface being provided at that side of said curtain which is downstream with reference to the direction of descent of said drop; and further comprising the step of directing some of said jets of liquid against said guide surface so that they sweep over and clean the same.

7. In an apparatus for producing filaments from viscous molten vitreous material, in combination, first means accommodating a body of viscous molten vitreou material, and being operative for exuding a drop of such material so that such drop will descend in a downward path under the influence of gravity and draw a length of filament behind it; second means including a rotary filament drawing surface, downwardly spaced from said first means and laterally spaced from said path; and third means for propelling a curtain of liquid under pressure transversely to and into said path of the descending drop at a velocity requisite for severing said drop and proximal filament portions from the remainder of said length of filament, while deflecting said remainder out of said path and into contact with said rotary filament drawing surface of said second means.

8. In an apparatus as defined in claim 7, wherein said third means comprises a guide surface extending transversely to said path and inclined in the direction of descent, and liquid-propelling means for propelling liquid in form of said curtain along said guide surface.

9. In an apparatus as defined in claim '8 said liquidpropelling means being operative for propelling said liquid in such a manner that said curtain is at least in part out of contact with said guide surface.

10. In an apparatus as defined in claim 8, said liquidpropelling means comprising at least one liquid conduit provided with at least one liquid-ejecting nozzle.

11. In an apparatus as defined in claim 8, said liquidpropelling means comprising at least one liquid conduit provided with a plurality of liquid-ejecting nozzles.

12. In an apparatus as defined in claim 8, said liquidpropelling means comprising at least one liquid conduit provided with a plurality of liquid-ejecting nozzles at least some of which are movable.

10 13. In an apparatus as defined in claim 8, said liquid- References Cited propelling means comprising at least one liquid conduit provided with a plurality of liquid-ejecting nozzles, some UNITED STATES PATENTS of said nozzles discharging in direction toward said guide 3,492,103 1/ 1970 Schuller et al. 65-10 surface and the remainder of said nozzles discharging in 5 3,506,419 4/1970, Smith et aL 5 at least substantial parallelism with said guide surface. 14. In an apparatus as defined in claim 10, and further S. LEON BASHORE, Primary Examiner comprising cover means covering said conduit at least in part against contact with said length of filament. LINDSAY, Assistant EXaminef 15. In an apparatus as defined in claim 14, said cover 10 means being upwardly spaced from and extending along U.S. Cl. X.R.

a portion of said guide surface defining therewith a gap, 6510 and said conduit being located in said gap between said cover means and said guide surface. 

